The present invention relates to fluoro-alcohol additives for orientation control of block copolymers used in directed self-assembly applications, and more specifically to materials for top orientation-control of high-chi (χ) block copolymers containing a polycarbonate block.
Block copolymers (BCPs) find many applications in solution, bulk and thin films. Thin film applications of BCPs are particularly attractive for nanolithography and patterning due to the ability of some BCPs to form periodic self-assembled structures ranging in feature size from 5 nm to 50 nm. The thin-film self-assembly property of BCPs can be utilized with existing photolithographic techniques to provide a unique approach to long range order for semiconductor applications. This approach, called directed self-assembly (DSA) of block copolymers, promises to extend the patterning capabilities of conventional lithography.
BCPs for directed self-assembly (DSA) applications comprise two or more polymer blocks that can phase separate into domains characterized by ordered nanoscopic arrays of spheres, cylinders, gyroids, and lamellae. The ability of a BCP to phase separate depends on the Flory Huggins interaction parameter chi (χ) and degree of polymerization of the block copolymer. Poly(styrene)-b-poly(methyl methacrylate), abbreviated as PS-b-PMMA, is the most widely used block copolymer for DSA. For PS-b-PMMA, the poly(styrene) block (PS) and the poly(methyl methacrylate) block (PMMA) have similar surface energies at the polymer-air interface at elevated temperatures. In this instance, annealing a thin layer of the BCP, which is disposed on an orientation control layer, induces phase separation to produce BCP domains that are perpendicularly oriented to the orientation control layer. Typically, for PS-b-PMMA the orientation control layer is a crosslinkable or brush-type random copolymer formed with styrene and methyl methacrylate. The neutral wetting properties of the orientation control layer (underlayer) can be controlled by adjusting the composition of styrene and methyl methacrylate in order to enable perpendicular orientation of the BCP lamellar domains.
The minimum half-pitch of PS-b-PMMA is limited to about 10 nm because of the lower interaction and interaction parameter chi (χ) between PS and PMMA. Typically when the product of chi and N of the block copolymer is less than 10, such a block copolymer tends to form disordered aggregates rather than ordered phase-separated domains. To enable further feature miniaturization (i.e., using block copolymers having lower degree of polymerization), a block copolymer with higher interaction parameter between two blocks (higher chi) is desirable. Several block copolymers having higher interaction parameter between the two blocks have been studied to obtain smaller feature sizes. Of particular interest are block copolymers comprising a block derived from ring opening of a cyclic carbonyl monomer from a reactive end-group on the first polymer block. Block copolymers formed by ring opening polymerization (ROP) of cyclic monomers (e.g., lactides, lactones, ethylene oxide) have been used to generate sub-10 nm feature size for patterning application.
As the interaction parameter between the two blocks of the block copolymer increases, neutral underlayer properties alone may not be sufficient for forming perpendicularly oriented block copolymer domains due to the increased mismatch between the polymer-air surface energies of the two blocks. This causes parallel orientation of the block copolymer domains with only the lower surface energy block present at the polymer-air interface, rendering the thin-film undesirable for lithographic applications. Top-coat based orientation control strategies have been employed to control the surface energy at the polymer-air interface of the blocks. However, these strategies introduce additional process complexity in the integration of high-chi block copolymers into standard lithography processes.
There exists a need to develop a top-coat free method for perpendicularly orienting block copolymer domains of a high-chi block copolymer with sub-10 nm half-pitch.